I have a use case where I need to implement a custom SocketImpl class and I've
run into some difficulty caused by the current design of SocketImpl and the
related classes in OpenJDK. My use case is implementing a custom proxy
protocol, similar in spirit to what SocksSocketImpl does but using a different
wire protocol. I need to be able to swap this proxy in underneath some
existing code that I can't modify, which is why I think a SocketImpl is the
appropriate solution rather than a SocketFactory (which would be much easier if
I could modify the code in question).
SocketImpl is a public class, so I think I'm fairly safe in assuming it's
intended as an extension point for application authors, but in practice it
seems very difficult to actually extend. Since I'm trying to accomplish
something very similar to what SocksSocketImpl does I'd like to take the same
approach that it and HttpConnectSocketImpl use of delegating all of the OS
interactions to the base PlainSocketImpl class and just adding the
customizations I need on top. However, I can't extend PlainSocketImpl the way
those other classes do because it is package-private and I can't create new
classes in java.net. Encapsulating a PlainSocketImpl doesn't really seem
viable either since all of the methods are also protected or package-private.
The alternatives I can see are to either implement a SocketImpl completely from
scratch (including all the native code) or to resort to classloader hacks to be
able to add a class to java.net which extends PlainSocketImpl. Neither of
those are particularly appealing.
I was going to ask whether it would be reasonable to make PlainSocketImpl
public, but reading through the net-dev archives[1] I discovered that there's
some refactoring[2] of SocketImpl that's happening right now to prepare for
Project Loom related work[3]. That change is introducing DelegatingSocketImpl
and PlatformSocketImpl classes and changes SocksSocketImpl and
HttpConnectSocketImpl to extend DelegatingSocketImpl rather than
PlainSocketImpl. I'd love to be able to extend DelegatingSocketImpl for my use
case, but it's package-private too, nor does there appear to be a way to get a
PlatformSocketImpl.
Is there any way that we could make it easier to implement a custom SocketImpl
(or am I missing some other possible approach)? If so, would it be reasonable
to make DelegatingSocketImpl public and introduce a DefaultSocketImplFactory
that can be used to construct a PlatformSocketImpl?
Thanks,
Jared
PS I just joined the net-dev mailing list, so there may be some historical
context I've missed.
[1] https://mail.openjdk.java.net/pipermail/net-dev/2019-March/012218.html
[2] http://cr.openjdk.java.net/~alanb/8220493/0/webrev/
[3] http://openjdk.java.net/jeps/8218559
